<template>
  <div>
    <h3>这个是son组件{{ a }}</h3>
    <button @click="hUpdate" />
  </div>
</template>

<script>
export default {
  props: {
    a: {
      type: Number,
      required: true
    }
  },
  methods: {
    hUpdate() {
      this.$emit('update:a', this.a + 1)
    }
  }
}
</script>
<style>
</style>
